Polymer bulk acoustic resonator

ABSTRACT

A polymer bulk acoustic resonator that includes an active semiconductor layer, a first thin film electrode layer applied to the semiconductor layer, a thin film electro-active polymer layer applied to the first thin film electrode layer; and a second thin film electrode layer applied to the thin film electro-active polymer layer.

BACKGROUND

The dielectric filter and Surface Acoustic Wave (SAW) filter are used incurrent wireless mobile telecommunication networks, including phonestypically referred to as cell phones. Recently, a new filter system offilm bulk acoustic resonator has been introduced. A thin film ofpiezoelectric material of ZnO is deposited on a substrate ofsemiconductor made of Si material, by using sputtering methods andMagnetron Sputtering Equipment. The sputtering methods require the useof a Magnetron and are a relatively expensive technique. Also, in orderto make an improve efficiency of energy coupling using a film bulkacoustic resonator, a Bragg Reflector is necessary between the ZnO layerand Si Substrate. The Bragg Reflector is usually made by depositingabout seven to eight layers alternatively of a very heavy material suchas Tungsten with the not so heavy layers of SiO2. This is necessary toprevent acoustic energy resonating loss from inside the piezoelectricthin film of ZnO. The acoustic energy resonating dissipates or leaks outbecause the magnitudes of two acoustic impedances of ZnO and Si aresimilar in order. Tungsten has an acoustic impedance of 10.1×10(7)Kg/m(2) s. SiO2 has an acoustic impedance of 1.31×10(7) Kg/m(2) s, whichis about 1/10 of that of Tungsten. The mismatch between two acousticimpedances of Tungsten and Si02 in the Bragg Reflector isolatesacoustically the active piezoelectric ZnO layer from the Si substrate.All depositions of layers for the film bulk acoustic resonator are doneby using the Magnetron. The film bulk acoustic resonator has potentialto be co-processed with active materials of semi-conductors such as Sior SiGe or GaAs. But, the use of film bulk acoustic resonator has a fewdifficulties to overcome and can be a quite expensive process tomanufacture. Also, resonant frequency is function of the thickness ofZnO in a film bulk acoustic resonator, therefore, uniformity of the ZnOthin film thickness is very important. It takes great care and expenseto obtain a uniform thin film of ZnO in the order 1/10 of 1 um.

SUMMARY OF THE INVENTION

A polymer bulk acoustic resonator that includes an active semiconductorlayer, a first thin film electrode layer applied to the semiconductorlayer, a thin film electro-active polymer layer applied to the firstthin film electrode layer; and a second thin film electrode layerapplied to the thin film electro-active polymer layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of circuit module according to the presentinvention.

FIG. 2 is a schematic view of polymer bulk acoustic resonator accordingto the present invention.

FIG. 3 is a schematic view of a step of making a polymer bulk acousticresonator according to the present invention.

FIG. 4 is a schematic view of a step of making a polymer bulk acousticresonator according to the present invention.

FIG. 5 is a schematic view of a step of making a polymer bulk acousticresonator according to the present invention.

FIG. 6 is a schematic view of a step of making a polymer bulk acousticresonator according to the present invention.

FIG. 7 is a schematic view of a step of making a polymer bulk acousticresonator according to the present invention.

FIG. 8 is a schematic view of a step of making a polymer bulk acousticresonator according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Integration between active components of semiconductors such as Silicon(Si), Silicon Germanium (SiGe), bipolar transistors, hetero-junctionbipolar transistors (HBTs), and high electron mobility transistors(HEMTs), and Gallium Arsenide (GaAs) field effect transistors, withpassive components such as high frequency filter elements, has beendesired for sometime. This is because of the desire to have futureappliances controlled by one control unit for home and personalelectronic equipment at anytime and anyplace, while including forcommunication capabilities and receiving broadcasts. FIG. 1 shows ablock schematic diagram of a circuit module including a filter bank withcontrol switches and amplifiers for use in wireless mobiletelecommunication equipment. Both the amplifiers and switches can beincluded as part of an active component semiconductor materials, such asSi, SiGe or GaAs, and the filter banks are made of dielectric materials.The active component semiconductor materials are used as signalprocessors which receive a frequency signal and respond to that signalwith a desired action. It is desired to have the dielectric materialswhich are used for the high frequency filters be co-processed with thesemiconductor materials to effectively integrated both into a monolithicmodule for wireless mobile telecommunication equipment. Integration ofthe dielectric and semiconductor materials into one functioning unitwill increase efficiency, reduce manufacturing cost and reduce spacerequire in electronic equipment, as compared to having separatecomponents used today.

The present invention is a polymer bulk acoustic resonator manufacturedto integrate the high frequency filters with the semiconductor materialsfor switches and amplifiers, as described above and shown in FIGS. 2-8.The polymer bulk acoustic resonator utilizes piezoelectricElectro-Active Polymers (EAP) as the thin film materials formanufacturing the polymer bulk acoustic resonator. The manufacture ofthe polymer bulk acoustic resonator employs a new approach in order toco-process active semiconductor materials such as Si, SiGe or GaAs withpassive high frequency filter piezoelectric polymer materials of EAP. Byusing EAP materials for passive filter devices, one can readily and costeffectively produce integrated modules of a passive filter bank alongwith active switches and amplifiers for wireless mobiletelecommunication network equipment. The operating frequency of thepolymer bulk acoustic resonator depends primarily on the thickness,density and bulk modulus of the EAP materials, which can be in the rangeof about 100 MHz to 30 GHz. The sound velocity (v) for EAP materialsranges from fifteen-hundred (1500) to two-thousand (2000) meters persecond. For a given resonant frequency f_(R), there is the equationf_(R)=v/(2*(thickness of the EAP)). Therefore, the thickness of EAPfilms for 1 GHz, 3 GHz, and 10 GHz resonant frequencies are 0.75 um,0.25 um, and 0.075 um, respectively. Usually, it is desired for thepolymer bulk acoustic resonator to allow passage of the quarterwavelength resonate of the desired frequency or frequencies.

Photolithography methods and spin casting techniques are used forsemiconductor fabrication and can be used to fabricate the polymer bulkacoustic resonator. Photolithography methods are used for cleaning thesemiconductor to receive other layers. Spin casting is used to applylayers of other materials to the semiconductor. Metals such as Aluminum(Al), Gold (Au), Platinum (Pt) and conductive polymer materials such aspoly-acetylene, polypyrrole, poly-aniline, polythiophene, and other highmolecular polymers can all be used as electrode materials in a liquidphase for the manufacture of the polymer bulk acoustic resonator.Electrodes and piezoelectric polymer thin film layers formed onsemiconductor substrates can be made by the spin casting the material onthe semiconductor. The spin casted materials are then cured bysolidifying thermally or by exposing the material to light energysources of ultra-violet light. The photolithograph method can be usedwith masking techniques and organic cleaning during manufacture of thepolymer bulk acoustic resonator to prepare the surface of thesemiconductor and other layers to receive the next layer. The spincasting technique scan be used to make both piezoelectric EAP layers andelectrode layers during the manufacturing of the polymer bulk acousticresonator. Note, that both EAP and electrode materials are available asliquid phases for use with spin casting techniques. By using the EAP asmaterials for the piezoelectric bulk acoustic resonator, the BraggReflector which is integrated in the film bulk acoustic resonator foruse in the active semiconductor based switch and amplifier circuits canbe eliminated. This is because the magnitudes of the acoustic impedanceof the EAP material is not similar to the semiconductor substratematerial. The evaporating of piezo-polymer and electrode layers bythermal or laser techniques can also be used to form the desired thinlayers of EAP, which can be co-processed with the active controlelements of switches and amplifiers on semiconductor substrates. Thethickness of spin casting the EAP and electrodes layers can becontrolled readily to provide the required uniformity at less cost thenusing the Magnetron method.

FIGS. 2-8 schematically show on the processing steps of one method ofmanufacturing the polymer bulk acoustic resonator. FIG. 2 shows aschematic diagram of a polymer bulk acoustic resonator. FIG. 1 shows thesemiconductor substrate layer 10 with a thin film bottom electrode layer12 stacked on top of the semiconductor substrate layer. A thin film EAPlayer 14 is stacked on top of the thin film bottom electrode layer 12. Athin film top electrode layer 16 is stacked on top of the thin film EAPlayer 14. Note, there is no air gap or Bragg Reflector required tominimize the acoustic energy loss from the EAP layer to semiconductorsubstrate layer. This is possible because of the excellent acousticimpedance mismatch between the EAP layer and semiconductor substratelayer.

FIG. 3 shows a schematic diagram of masking the semiconductor substratelayer 10 for photolithograph and organic cleaning. FIG. 4 shows aschematic diagram of the bottom electrode layer 12 being laid down uponthe semiconductor substrate layer 10. FIG. 5 shows a schematic diagramof masking the semiconductor substrate layer 10 again in preparation forcleaning and adding the EAP layer 14. FIG. 6 shows a schematic diagramof the EAP layer 14 being laid down on the bottom electrode layer 12.FIG. 7 shows a schematic diagram of masking the semiconductor substratelayer 10 again for cleaning and adding the top electrode layer 16. FIG.8 shows a schematic diagram of the top electrode layer 16 being laiddown on top of the EAP layer 14.

While different embodiments of the invention have been described indetail herein, it will be appreciated by those skilled in the art thatvarious modifications and alternatives to the embodiments could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular arrangements are illustrative only and arenot limiting as to the scope of the invention that is to be given thefull breadth of any and all equivalents thereof.

1. A polymer bulk acoustic resonator comprising: an active semiconductorlayer; a first thin film electrode layer applied to said semiconductorlayer; a thin film electro-active polymer layer applied to said firstthin film electrode layer; and a second thin film electrode layerapplied to said thin film electro-active polymer layer.
 2. The polymerbulk acoustic resonator of claim 1, wherein acoustic impedance of saidelectro-active polymer layer is not similar to acoustic impedance ofsaid semiconductor layer.
 3. The polymer bulk acoustic resonator ofclaim 1, wherein said semiconductor layer includes at least one switchand said electro-active polymer layer is a frequency signal filter. 4.The polymer bulk acoustic resonator of claim 1, wherein saidsemiconductor layer includes at least one amplifier and saidelectro-active polymer layer is a frequency signal filter.
 5. Thepolymer bulk acoustic resonator of claim 1, wherein said semiconductorlayer includes at least one signal processor and said electro-activepolymer layer is a frequency signal filter.
 6. A filter switch bankmodule comprising: an active semiconductor layer with switchingcapability; a first thin film electrode layer applied to saidsemiconductor layer; a thin film electro-active polymer layer applied tosaid first thin film electrode layer with frequency signal filteringcapability; and a second thin film electrode layer applied to said thinfilm electro-active polymer layer.
 7. The filter switch bank module ofclaim 6, wherein said active semiconductor layer also includes at leastone amplifier integrated as part of said active semiconductor layer.